Catherine "Cathy" O'Sullivan was the wife of Patrick O'Sullivan and the mother of the Eighth Doctor's companion Molly O'Sullivan (AUDIO: Tangled Web) and had seven other children, all of whom she outlived. (AUDIO: Fugitives, X and the Daleks) Two of her sons and three of her daughters died before their fifth birthdays. She had two other sons, Patrick and Liam. Patrick joined the British Army during World War I and was killed on his first day in France while Liam remained in Ireland but was killed by an English sentry. (AUDIO: X and the Daleks)
While serving as a Voluntary Aid Detachment nursing assistant in France during World War I, Molly frequently wrote letters to her mother, who lived in London. (AUDIO: The Great War) After travelling to Dunkirk on 29 May 1940 in the TARDIS, Molly continued writing a letter which she was going to post to her mother prior to leaving her own time. She began to tell her mother of her trip to the future but ultimately abandoned the letter as the whole story sounded preposterous. (AUDIO: Fugitives) Molly eventually finished her letter and intended to post the letter after leaving the Doctor and returning to her own time. (AUDIO: X and the Daleks)
Cathy disapproved of Molly's grandmother's palm-reading. (AUDIO: The Death of Hope)